In manufacturing semiconductor devices such as LSI and super-LSI or in manufacturing a liquid crystal display board, a pattern is made by irradiating a light to a semiconductor wafer or an original plate for liquid crystal; however, if a dust adheres to a mask for lithography (also simply referred to as “mask”) or a reticle (these are collectively referred to as “exposure original plate” herein below), the dust absorbs light or bends it, causing deformation of a transferred pattern, roughened edges or black stains on a base, and leads to problems of damaged dimensions, poor quality, deformed appearance and the like.
The above-mentioned manufacturing of semiconductor devices and liquid crystal display board are usually performed in a clean room, but even so, it is still difficult to keep the exposure original plate clean all the time; therefore, in general the light irradiation is carried out only after a surface of the exposure original plate is sheltered by a pellicle. In this way, the dust particle is prevented from directly adhering to the surface of the exposure original plate but is caught on the pellicle, and if, at the time of the lithography, the exposure light is focused on the pattern described on the exposure original plate the dust particle on the pellicle fails to affect the image transferring.
As shown in FIG. 1 as well as FIG. 3, a pellicle is basically built up of a pellicle frame 3, a transparent pellicle membrane 2, which is attached tensely to an upper annular face of the pellicle frame 3, and an agglutinant layer 4 formed on a lower annular face of the pellicle frame 3 for enabling the pellicle to be adhered to a mask or an exposure original plate.
The pellicle membrane 2 is made of cellulose nitrate, cellulose acetate and a fluorine-containing polymer or the like which transmit well such lights of mercury lamp that are used in light exposure (e.g., g-line [436 nm], i-line [365 nm], KrF excimer laser [248 nm], and ArF excimer laser [193 nm]). To attach the pellicle membrane 2 to the pellicle frame 3, a solvent that dissolves the pellicle membrane well is applied to the upper annular face of the frame 3 and, after pasting the pellicle membrane 2 on it, the solvent and the membrane are dried by air flow, or alternatively an adhesive agent such as acrylic resin, epoxy resin and fluorine-containing resin is used to fix the pellicle membrane 2 on the upper annular face. On the other hand, the lower annular face of the pellicle frame 3 is laid with an agglutinant layer 4 made of a polybutene resin, a polyvinyl acetate resin, an acrylic resin and a silicone resin or the like for enabling the pellicle frame 3 to be adhered to the exposure original plate, and on this agglutinant layer 4 is laid a releasable liner for protecting the agglutinant layer 4, if it is required.
The pellicle as described above is installed for the purpose of preventing the dust from adhering to the mask; consequently, it is preferable that the pellicle itself is kept free of dust, and hence it is common that the pellicle is stored in a container 1 specially made for pellicle during preservation or transportation. FIG. 3 shows how a pellicle sits on a mount 6 in a pellicle container made of a resin.
In recent years, however, the design rule for LSI has progressed to require as high a resolution as sub-quarter micron order, and correspondingly as this, shortening of the wavelength of exposure light source is in progress. For this reason, the choice of the exposure light source is shifting from the heretofore commonly used mercury lamp, which emits g-line [436 nm] and i-line [365 nm], to KrF excimer laser [248 nm] and ArF excimer laser [193 nm]) or the like. As the wavelength of the exposure light is shortened, the influence of the deformation of the mask upon the quality of the transferred lithographic image is becoming a greater problem, and therefore the flatness demanded of the mask has been heightening.
One of the factors that affect the flatness of the mask is the flatness of the pellicle which is adhered to the mask, and to address this, IP Publication 1 teaches to make the flatness of the agglutinant layer of the pellicle frame to be 15 micrometers or smaller so as to reduce the deformation of the mask induced by the pellicle as it is adhered to the mask.
However, even though the flatness of the agglutinant layer of the pellicle frame is improved, there are still instances wherein deformation occurs in the lithographic image at the time of exposure by short-wavelength light—hence the problem is not yet solved.
[Prior Art]
[IP Publication]
[IP Publication 1]
Japanese Patent Application Publication 2012-108277